// SPDX-License-Identifier: GPL-2.0

/* In-place tunneling */

#include <vmlinux.h>

#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include "bpf_tracing_net.h"
#include "bpf_compiler.h"

#pragma GCC diagnostic ignored "-Waddress-of-packed-member"

static const int cfg_port = 8000;

static const int cfg_udp_src = 20000;

#define ETH_P_MPLS_UC   0x8847
#define ETH_P_TEB       0x6558

#define MPLS_LS_S_MASK  0x00000100
#define BPF_F_ADJ_ROOM_ENCAP_L2(len)                    \
        (((__u64)len & BPF_ADJ_ROOM_ENCAP_L2_MASK)      \
         << BPF_ADJ_ROOM_ENCAP_L2_SHIFT)

struct vxlanhdr___local {
        __be32 vx_flags;
        __be32 vx_vni;
};

#define L2_PAD_SZ       (sizeof(struct vxlanhdr___local) + ETH_HLEN)

#define UDP_PORT                5555
#define MPLS_OVER_UDP_PORT      6635
#define ETH_OVER_UDP_PORT       7777
#define VXLAN_UDP_PORT          8472

#define EXTPROTO_VXLAN  0x1

#define VXLAN_FLAGS     bpf_htonl(1<<27)
#define VNI_ID          1
#define VXLAN_VNI       bpf_htonl(VNI_ID << 8)

#ifndef NEXTHDR_DEST
#define NEXTHDR_DEST    60
#endif

/* MPLS label 1000 with S bit (last label) set and ttl of 255. */
static const __u32 mpls_label = __bpf_constant_htonl(1000 << 12 |
                                                     MPLS_LS_S_MASK | 0xff);
struct gre_hdr {
        __be16 flags;
        __be16 protocol;
} __attribute__((packed));

union l4hdr {
        struct udphdr udp;
        struct gre_hdr gre;
};

struct v4hdr {
        struct iphdr ip;
        union l4hdr l4hdr;
        __u8 pad[L2_PAD_SZ];            /* space for L2 header / vxlan header ... */
} __attribute__((packed));

struct v6hdr {
        struct ipv6hdr ip;
        union l4hdr l4hdr;
        __u8 pad[L2_PAD_SZ];            /* space for L2 header / vxlan header ... */
} __attribute__((packed));

static __always_inline void set_ipv4_csum(struct iphdr *iph)
{
        __u16 *iph16 = (__u16 *)iph;
        __u32 csum;
        int i;

        iph->check = 0;

        __pragma_loop_unroll_full
        for (i = 0, csum = 0; i < sizeof(*iph) >> 1; i++)
                csum += *iph16++;

        iph->check = ~((csum & 0xffff) + (csum >> 16));
}

static __always_inline int __encap_ipv4(struct __sk_buff *skb, __u8 encap_proto,
                                        __u16 l2_proto, __u16 ext_proto)
{
        struct iphdr iph_inner = {0};
        __u16 udp_dst = UDP_PORT;
        struct v4hdr h_outer;
        struct tcphdr tcph;
        int olen, l2_len;
        __u8 *l2_hdr = NULL;
        int tcp_off;
        __u64 flags;

        /* Most tests encapsulate a packet into a tunnel with the same
         * network protocol, and derive the outer header fields from
         * the inner header.
         *
         * The 6in4 case tests different inner and outer protocols. As
         * the inner is ipv6, but the outer expects an ipv4 header as
         * input, manually build a struct iphdr based on the ipv6hdr.
         */
        if (encap_proto == IPPROTO_IPV6) {
                const __u32 saddr = (192 << 24) | (168 << 16) | (1 << 8) | 1;
                const __u32 daddr = (192 << 24) | (168 << 16) | (1 << 8) | 2;
                struct ipv6hdr iph6_inner;

                /* Read the IPv6 header */
                if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph6_inner,
                                       sizeof(iph6_inner)) < 0)
                        return TC_ACT_OK;

                /* Derive the IPv4 header fields from the IPv6 header */
                iph_inner.version = 4;
                iph_inner.ihl = 5;
                iph_inner.tot_len = bpf_htons(sizeof(iph6_inner) +
                                    bpf_ntohs(iph6_inner.payload_len));
                iph_inner.ttl = iph6_inner.hop_limit - 1;
                iph_inner.protocol = iph6_inner.nexthdr;
                iph_inner.saddr = __bpf_constant_htonl(saddr);
                iph_inner.daddr = __bpf_constant_htonl(daddr);

                tcp_off = sizeof(iph6_inner);
        } else {
                if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_inner,
                                       sizeof(iph_inner)) < 0)
                        return TC_ACT_OK;

                tcp_off = sizeof(iph_inner);
        }

        /* filter only packets we want */
        if (iph_inner.ihl != 5 || iph_inner.protocol != IPPROTO_TCP)
                return TC_ACT_OK;

        if (bpf_skb_load_bytes(skb, ETH_HLEN + tcp_off,
                               &tcph, sizeof(tcph)) < 0)
                return TC_ACT_OK;

        if (tcph.dest != __bpf_constant_htons(cfg_port))
                return TC_ACT_OK;

        olen = sizeof(h_outer.ip);
        l2_len = 0;

        flags = BPF_F_ADJ_ROOM_FIXED_GSO | BPF_F_ADJ_ROOM_ENCAP_L3_IPV4;

        switch (l2_proto) {
        case ETH_P_MPLS_UC:
                l2_len = sizeof(mpls_label);
                udp_dst = MPLS_OVER_UDP_PORT;
                break;
        case ETH_P_TEB:
                l2_len = ETH_HLEN;
                if (ext_proto & EXTPROTO_VXLAN) {
                        udp_dst = VXLAN_UDP_PORT;
                        l2_len += sizeof(struct vxlanhdr___local);
                } else
                        udp_dst = ETH_OVER_UDP_PORT;
                break;
        }
        flags |= BPF_F_ADJ_ROOM_ENCAP_L2(l2_len);

        switch (encap_proto) {
        case IPPROTO_GRE:
                flags |= BPF_F_ADJ_ROOM_ENCAP_L4_GRE;
                olen += sizeof(h_outer.l4hdr.gre);
                h_outer.l4hdr.gre.protocol = bpf_htons(l2_proto);
                h_outer.l4hdr.gre.flags = 0;
                break;
        case IPPROTO_UDP:
                flags |= BPF_F_ADJ_ROOM_ENCAP_L4_UDP;
                olen += sizeof(h_outer.l4hdr.udp);
                h_outer.l4hdr.udp.source = __bpf_constant_htons(cfg_udp_src);
                h_outer.l4hdr.udp.dest = bpf_htons(udp_dst);
                h_outer.l4hdr.udp.check = 0;
                h_outer.l4hdr.udp.len = bpf_htons(bpf_ntohs(iph_inner.tot_len) +
                                                  sizeof(h_outer.l4hdr.udp) +
                                                  l2_len);
                break;
        case IPPROTO_IPIP:
        case IPPROTO_IPV6:
                break;
        default:
                return TC_ACT_OK;
        }

        /* add L2 encap (if specified) */
        l2_hdr = (__u8 *)&h_outer + olen;
        switch (l2_proto) {
        case ETH_P_MPLS_UC:
                *(__u32 *)l2_hdr = mpls_label;
                break;
        case ETH_P_TEB:
                flags |= BPF_F_ADJ_ROOM_ENCAP_L2_ETH;

                if (ext_proto & EXTPROTO_VXLAN) {
                        struct vxlanhdr___local *vxlan_hdr = (struct vxlanhdr___local *)l2_hdr;

                        vxlan_hdr->vx_flags = VXLAN_FLAGS;
                        vxlan_hdr->vx_vni = VXLAN_VNI;

                        l2_hdr += sizeof(struct vxlanhdr___local);
                }

                if (bpf_skb_load_bytes(skb, 0, l2_hdr, ETH_HLEN))
                        return TC_ACT_SHOT;

                break;
        }
        olen += l2_len;

        /* add room between mac and network header */
        if (bpf_skb_adjust_room(skb, olen, BPF_ADJ_ROOM_MAC, flags))
                return TC_ACT_SHOT;

        /* prepare new outer network header */
        h_outer.ip = iph_inner;
        h_outer.ip.tot_len = bpf_htons(olen +
                                       bpf_ntohs(h_outer.ip.tot_len));
        h_outer.ip.protocol = encap_proto;

        set_ipv4_csum((void *)&h_outer.ip);

        /* store new outer network header */
        if (bpf_skb_store_bytes(skb, ETH_HLEN, &h_outer, olen,
                                BPF_F_INVALIDATE_HASH) < 0)
                return TC_ACT_SHOT;

        /* if changing outer proto type, update eth->h_proto */
        if (encap_proto == IPPROTO_IPV6) {
                struct ethhdr eth;

                if (bpf_skb_load_bytes(skb, 0, &eth, sizeof(eth)) < 0)
                        return TC_ACT_SHOT;
                eth.h_proto = bpf_htons(ETH_P_IP);
                if (bpf_skb_store_bytes(skb, 0, &eth, sizeof(eth), 0) < 0)
                        return TC_ACT_SHOT;
        }

        return TC_ACT_OK;
}

static __always_inline int encap_ipv4(struct __sk_buff *skb, __u8 encap_proto,
                                      __u16 l2_proto)
{
        return __encap_ipv4(skb, encap_proto, l2_proto, 0);
}

static __always_inline int __encap_ipv6(struct __sk_buff *skb, __u8 encap_proto,
                                        __u16 l2_proto, __u16 ext_proto)
{
        __u16 udp_dst = UDP_PORT;
        struct ipv6hdr iph_inner;
        struct v6hdr h_outer;
        struct tcphdr tcph;
        int olen, l2_len;
        __u8 *l2_hdr = NULL;
        __u16 tot_len;
        __u64 flags;

        if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_inner,
                               sizeof(iph_inner)) < 0)
                return TC_ACT_OK;

        /* filter only packets we want */
        if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(iph_inner),
                               &tcph, sizeof(tcph)) < 0)
                return TC_ACT_OK;

        if (tcph.dest != __bpf_constant_htons(cfg_port))
                return TC_ACT_OK;

        olen = sizeof(h_outer.ip);
        l2_len = 0;

        flags = BPF_F_ADJ_ROOM_FIXED_GSO | BPF_F_ADJ_ROOM_ENCAP_L3_IPV6;

        switch (l2_proto) {
        case ETH_P_MPLS_UC:
                l2_len = sizeof(mpls_label);
                udp_dst = MPLS_OVER_UDP_PORT;
                break;
        case ETH_P_TEB:
                l2_len = ETH_HLEN;
                if (ext_proto & EXTPROTO_VXLAN) {
                        udp_dst = VXLAN_UDP_PORT;
                        l2_len += sizeof(struct vxlanhdr___local);
                } else
                        udp_dst = ETH_OVER_UDP_PORT;
                break;
        }
        flags |= BPF_F_ADJ_ROOM_ENCAP_L2(l2_len);

        switch (encap_proto) {
        case IPPROTO_GRE:
                flags |= BPF_F_ADJ_ROOM_ENCAP_L4_GRE;
                olen += sizeof(h_outer.l4hdr.gre);
                h_outer.l4hdr.gre.protocol = bpf_htons(l2_proto);
                h_outer.l4hdr.gre.flags = 0;
                break;
        case IPPROTO_UDP:
                flags |= BPF_F_ADJ_ROOM_ENCAP_L4_UDP;
                olen += sizeof(h_outer.l4hdr.udp);
                h_outer.l4hdr.udp.source = __bpf_constant_htons(cfg_udp_src);
                h_outer.l4hdr.udp.dest = bpf_htons(udp_dst);
                tot_len = bpf_ntohs(iph_inner.payload_len) + sizeof(iph_inner) +
                          sizeof(h_outer.l4hdr.udp) + l2_len;
                h_outer.l4hdr.udp.check = 0;
                h_outer.l4hdr.udp.len = bpf_htons(tot_len);
                break;
        case IPPROTO_IPV6:
                break;
        default:
                return TC_ACT_OK;
        }

        /* add L2 encap (if specified) */
        l2_hdr = (__u8 *)&h_outer + olen;
        switch (l2_proto) {
        case ETH_P_MPLS_UC:
                *(__u32 *)l2_hdr = mpls_label;
                break;
        case ETH_P_TEB:
                flags |= BPF_F_ADJ_ROOM_ENCAP_L2_ETH;

                if (ext_proto & EXTPROTO_VXLAN) {
                        struct vxlanhdr___local *vxlan_hdr = (struct vxlanhdr___local *)l2_hdr;

                        vxlan_hdr->vx_flags = VXLAN_FLAGS;
                        vxlan_hdr->vx_vni = VXLAN_VNI;

                        l2_hdr += sizeof(struct vxlanhdr___local);
                }

                if (bpf_skb_load_bytes(skb, 0, l2_hdr, ETH_HLEN))
                        return TC_ACT_SHOT;
                break;
        }
        olen += l2_len;

        /* add room between mac and network header */
        if (bpf_skb_adjust_room(skb, olen, BPF_ADJ_ROOM_MAC, flags))
                return TC_ACT_SHOT;

        /* prepare new outer network header */
        h_outer.ip = iph_inner;
        h_outer.ip.payload_len = bpf_htons(olen +
                                           bpf_ntohs(h_outer.ip.payload_len));

        h_outer.ip.nexthdr = encap_proto;

        /* store new outer network header */
        if (bpf_skb_store_bytes(skb, ETH_HLEN, &h_outer, olen,
                                BPF_F_INVALIDATE_HASH) < 0)
                return TC_ACT_SHOT;

        return TC_ACT_OK;
}

static int encap_ipv6_ipip6(struct __sk_buff *skb)
{
        struct v6hdr h_outer = {0};
        struct iphdr iph_inner;
        struct tcphdr tcph;
        struct ethhdr eth;
        __u64 flags;
        int olen;

        if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_inner,
                               sizeof(iph_inner)) < 0)
                return TC_ACT_OK;

        /* filter only packets we want */
        if (bpf_skb_load_bytes(skb, ETH_HLEN + (iph_inner.ihl << 2),
                               &tcph, sizeof(tcph)) < 0)
                return TC_ACT_OK;

        if (tcph.dest != __bpf_constant_htons(cfg_port))
                return TC_ACT_OK;

        olen = sizeof(h_outer.ip);

        flags = BPF_F_ADJ_ROOM_FIXED_GSO | BPF_F_ADJ_ROOM_ENCAP_L3_IPV6;

        /* add room between mac and network header */
        if (bpf_skb_adjust_room(skb, olen, BPF_ADJ_ROOM_MAC, flags))
                return TC_ACT_SHOT;

        /* prepare new outer network header */
        h_outer.ip.version = 6;
        h_outer.ip.hop_limit = iph_inner.ttl;
        h_outer.ip.saddr.in6_u.u6_addr8[1] = 0xfd;
        h_outer.ip.saddr.in6_u.u6_addr8[15] = 1;
        h_outer.ip.daddr.in6_u.u6_addr8[1] = 0xfd;
        h_outer.ip.daddr.in6_u.u6_addr8[15] = 2;
        h_outer.ip.payload_len = iph_inner.tot_len;
        h_outer.ip.nexthdr = IPPROTO_IPIP;

        /* store new outer network header */
        if (bpf_skb_store_bytes(skb, ETH_HLEN, &h_outer, olen,
                                BPF_F_INVALIDATE_HASH) < 0)
                return TC_ACT_SHOT;

        /* update eth->h_proto */
        if (bpf_skb_load_bytes(skb, 0, &eth, sizeof(eth)) < 0)
                return TC_ACT_SHOT;
        eth.h_proto = bpf_htons(ETH_P_IPV6);
        if (bpf_skb_store_bytes(skb, 0, &eth, sizeof(eth), 0) < 0)
                return TC_ACT_SHOT;

        return TC_ACT_OK;
}

static __always_inline int encap_ipv6(struct __sk_buff *skb, __u8 encap_proto,
                                      __u16 l2_proto)
{
        return __encap_ipv6(skb, encap_proto, l2_proto, 0);
}

SEC("tc")
int __encap_ipip_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_IPIP, ETH_P_IP);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_gre_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_GRE, ETH_P_IP);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_gre_mpls(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_GRE, ETH_P_MPLS_UC);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_gre_eth(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_GRE, ETH_P_TEB);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_udp_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_UDP, ETH_P_IP);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_udp_mpls(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_UDP, ETH_P_MPLS_UC);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_udp_eth(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv4(skb, IPPROTO_UDP, ETH_P_TEB);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_vxlan_eth(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return __encap_ipv4(skb, IPPROTO_UDP,
                                    ETH_P_TEB,
                                    EXTPROTO_VXLAN);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_sit_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv4(skb, IPPROTO_IPV6, ETH_P_IP);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6tnl_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_IPV6, ETH_P_IPV6);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ipip6_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
                return encap_ipv6_ipip6(skb);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6gre_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_GRE, ETH_P_IPV6);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6gre_mpls(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_GRE, ETH_P_MPLS_UC);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6gre_eth(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_GRE, ETH_P_TEB);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6udp_none(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_UDP, ETH_P_IPV6);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6udp_mpls(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_UDP, ETH_P_MPLS_UC);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6udp_eth(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return encap_ipv6(skb, IPPROTO_UDP, ETH_P_TEB);
        else
                return TC_ACT_OK;
}

SEC("tc")
int __encap_ip6vxlan_eth(struct __sk_buff *skb)
{
        if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
                return __encap_ipv6(skb, IPPROTO_UDP,
                                    ETH_P_TEB,
                                    EXTPROTO_VXLAN);
        else
                return TC_ACT_OK;
}

static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
{
        __u64 flags = BPF_F_ADJ_ROOM_FIXED_GSO;
        struct ipv6_opt_hdr ip6_opt_hdr;
        struct gre_hdr greh;
        struct udphdr udph;
        int olen = len;

        switch (proto) {
        case IPPROTO_IPIP:
                flags |= BPF_F_ADJ_ROOM_DECAP_L3_IPV4;
                break;
        case IPPROTO_IPV6:
                flags |= BPF_F_ADJ_ROOM_DECAP_L3_IPV6;
                break;
        case NEXTHDR_DEST:
                if (bpf_skb_load_bytes(skb, off + len, &ip6_opt_hdr,
                                       sizeof(ip6_opt_hdr)) < 0)
                        return TC_ACT_OK;
                switch (ip6_opt_hdr.nexthdr) {
                case IPPROTO_IPIP:
                        flags |= BPF_F_ADJ_ROOM_DECAP_L3_IPV4;
                        break;
                case IPPROTO_IPV6:
                        flags |= BPF_F_ADJ_ROOM_DECAP_L3_IPV6;
                        break;
                default:
                        return TC_ACT_OK;
                }
                break;
        case IPPROTO_GRE:
                olen += sizeof(struct gre_hdr);
                if (bpf_skb_load_bytes(skb, off + len, &greh, sizeof(greh)) < 0)
                        return TC_ACT_OK;
                switch (bpf_ntohs(greh.protocol)) {
                case ETH_P_MPLS_UC:
                        olen += sizeof(mpls_label);
                        break;
                case ETH_P_TEB:
                        olen += ETH_HLEN;
                        break;
                }
                break;
        case IPPROTO_UDP:
                olen += sizeof(struct udphdr);
                if (bpf_skb_load_bytes(skb, off + len, &udph, sizeof(udph)) < 0)
                        return TC_ACT_OK;
                switch (bpf_ntohs(udph.dest)) {
                case MPLS_OVER_UDP_PORT:
                        olen += sizeof(mpls_label);
                        break;
                case ETH_OVER_UDP_PORT:
                        olen += ETH_HLEN;
                        break;
                case VXLAN_UDP_PORT:
                        olen += ETH_HLEN + sizeof(struct vxlanhdr___local);
                        break;
                }
                break;
        default:
                return TC_ACT_OK;
        }

        if (bpf_skb_adjust_room(skb, -olen, BPF_ADJ_ROOM_MAC, flags))
                return TC_ACT_SHOT;

        return TC_ACT_OK;
}

static int decap_ipv4(struct __sk_buff *skb)
{
        struct iphdr iph_outer;

        if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_outer,
                               sizeof(iph_outer)) < 0)
                return TC_ACT_OK;

        if (iph_outer.ihl != 5)
                return TC_ACT_OK;

        return decap_internal(skb, ETH_HLEN, sizeof(iph_outer),
                              iph_outer.protocol);
}

static int decap_ipv6(struct __sk_buff *skb)
{
        struct ipv6hdr iph_outer;

        if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_outer,
                               sizeof(iph_outer)) < 0)
                return TC_ACT_OK;

        return decap_internal(skb, ETH_HLEN, sizeof(iph_outer),
                              iph_outer.nexthdr);
}

SEC("tc")
int decap_f(struct __sk_buff *skb)
{
        switch (skb->protocol) {
        case __bpf_constant_htons(ETH_P_IP):
                return decap_ipv4(skb);
        case __bpf_constant_htons(ETH_P_IPV6):
                return decap_ipv6(skb);
        default:
                /* does not match, ignore */
                return TC_ACT_OK;
        }
}

char __license[] SEC("license") = "GPL";